How to use TF1 with variables?


I’m having trouble learning how to use the TF1 function properly, due to my unfamiliarity with coding. I want to add some modifiers to a Poisson function.
So a standard function would be

void fplot()
	TF1 *Poisson0 = new TF1("Poisson0","TMath::Poisson(0,x)",0,10);
	Poisson0 -> Draw();

But I need to modify the Poisson curve by giving it a amplitude multiplier which would be Var0 in this case. And to explode the x-axis by another variable “Var1”
So I tried doing this

void fplot()
	double Var0 = 5000;
	double Var1 = 1e12;
	TF1 *Poisson0 = new TF1("Poisson0","Var0*TMath::Poisson(0,x/Var1)",0,Var1*10);
	Poisson0 -> Draw();

But an error where Var0 and Var1 is considered unknown is spat out. If anyone can educate me on how to solve this, your help would be greatly appreciated.


___ROOT Version: 6.24
_Platform: Windows
Compiler: Not Provided

One possibility:

  TF1 *Poisson0 = new TF1("Poisson0", "[Var0]*TMath::Poisson(0.,x/[Var1])", 0., 10.);
  // Poisson0->Print();
  double Var0 = 5000., Var1 = 1.e12;
  Poisson0->SetParameters(Var0, Var1); Poisson0->SetRange(0., Var1 * 10.);

Whoa that worked, thanks!!
Just wondering what does the period after the parameters mean?
like 0., 10., etc etc.

It means these numbers are floating point numbers. Without a period it would mean they are integers.